Fingerprint powders are fine powders used in dusting for fingerprints, for instance, by crime scene investigators and others in law enforcement. The process of dusting for fingerprints involves various methods intended to get the particles of the powder to adhere to residue left by friction ridge skin on the fingers, palms, or feet. Physical development of fingerprints using powders is just one of various methods used to develop fingerprints. Fingerprints often leave residues of oils in the shape of the friction ridges, but the friction ridge skin itself does not secrete oils. For this reason, some fingerprints will only leave a residue of amino acids and other compounds to which the powder does not adhere. Dusting is used as part of an array of techniques to develop fingerprints. Dusting is often used on larger areas in a crime scene which cannot be removed for analysis.
Powders may be applied with a fingerprint brush, which is a brush with extremely fine fibers designed to hold powder and deposit it gently on the fingerprint to be revealed without rubbing away the often delicate residue of the fingerprint itself. Powders may also be applied by blowing the powder across the fingerprint, or by pouring the powder onto the print, and then blowing away the excess. Historically, lycopodium powder—that is, spores of mosses, ground cedar, and the like—was used as a fingerprint powder. Modern fingerprint powders have a variety of compositions, including for example aluminum powder, aluminum flakes, and lampblack.
Factors influencing the effectiveness of fingerprint powders include fineness (the powder must be fine enough to show the detail of the fingerprint), adhesion (the powder should adhere to the residue of the fingerprint and not adhere to the rest of the surface so as to obscure the view of the print), color (the fingerprint powder should be a suitable color for the surface in question), and flowability (the powder should not cake into a solid).
Some surfaces, such as organic ones, do not lend themselves to the use of fingerprint powders, so that use of alternate methods is necessary. Other media, such as certain types of glue, can be “smoked” over these surfaces to develop the latent fingerprints thereupon. For instance, when the specimen is a metallic weapon such as a handgun or a knife, synthetic leather, or an adhesive face of an adhesive tape, dusting with powder cannot copy the fingerprint clearly. Instead, methods in which 2-cyanoacrylate is vaporized and converted via moisture on a fingerprint to a polymer have been used as a method for developing a fingerprint residue more clearly. Conventionally, such fingerprint detection has been conducted with what is, in effect, liquid cyanoacrylate glue.
The detection of fingerprint using 2-cyanoacrylate is usually carried out by means of allowing a vapor of 2-cyanoacrylate (monomer) to adhere to a fingerprint. For instance, 2-cyanoacrylate (monomer) may be sprayed onto latent fingerprints or impregnated into woven or nonwoven fabric and allowed to volatilize onto the latent fingerprints. Another known method involves simultaneous use of vapors of 2-cyanoacrylate (monomer) and a sublimation dye, to colorize the fingerprint detection when the fingerprints are present on a white or silvery colored metallic surface.
U.S. Pat. No. 8,268,919 (Shimoda) discloses the preparation of crushed powder mixtures for use in detecting fingerprints. The claims of the Shimoda patent recite a composition for detecting fingerprints, which composition comprises a 2-cyanoacrylate polymer polymerized by use of a specified type of polymerization initiator. Shimoda also discloses the use of polymers obtained by reacting a 2-cyanoacrylate with specific fluorescent colorants which act as polymerization initiators.
Weaver (U.S. Pat. No. 5,348,759) discloses a device that can be used to detect latent prints in a variety of locations, including outdoors. The device has a housing which holds a quantity of solid granulated cyanoacrylate. The Weaver patent does not provide any details regarding the nature of the solid granulated cyanoacrylate. The cyanoacrylate is placed around the periphery of the housing. One end of the housing is tapered to form a connecting tube, and the connecting tube is placed on the end of a propane torch. The torch is used to vaporize the cyanoacrylate in the housing into a vapor. The vapor is then propelled forward from the torch by the velocity of the torch exhaust gases, and projected onto the test object, which causes latent prints to appear.